Thyristor with "on" protective circuit and darlington output stage

Abstract

A thyristor is preferably fabricated as a single thyristor device in an integrated circuit. The thyristor is made conductive by applying an ordinary gating voltage to the gate thereof. However, the thyristor can be kept in a conductive state, even though a current flowing through the anode and cathode thereof is stopped, if the current is restored to flow through it again within a predetermined short time after has stopped. The thyristor is composed of a first transistor and a second transistor (both of which are also used in a typical thyristor component) a third transistor which forms a Darlington connection with the second transistor, a resistor which is connected between the base and the emitter of the third transistor, and a capacitor which is connected between the base of the second transistor and the emitter of the third transistor.

What is claimed is: 
     
       1. A circuit including an anode, a cathode and a gate, said circuit connected to a power supply and ground via the anode and the cathode, said circuit comprising: a first transistor comprising a base, a first terminal connected to said gate, and second terminal connected to a selected one of said anode and said cathode;   a second transistor comprising a first terminal connected to the base of the first transistor, a second terminal, and a base connected to the gate;   a third transistor having a first terminal connected to the first terminal of said second transistor, a second terminal connected to the other of said anode and said cathode, and a base connected to the second terminal of said second transistor;   a resistor, having a first end connected to the second terminal of said third transistor and a second end connected to the second terminal of said second transistor and the base of said third transistor to form a common node therewith, the common node being exclusively connected to said resistor and said second and third transistors; and   a capacitor connected between said gate and the other of said anode and said cathode;   said second transistor being responsive to a gating voltage applied to said gate with respect to ground, said second transistor thereby being rendered conductive and, during initial turn-on of said first transistor as a result of conduction of said second transistor, establishing the following voltage relationship:   V.sub.G1 =V.sub.BE2 +R·I.sub.E2 ≈V.sub.BE2     where V G1  is a gate voltage applied to said gate, V BE2  is a voltage difference between the base and the second terminal of said second transistor, R is a resistance value of said resistor and I E2  is a current passing through the second terminal of said second transistor during initial turn-on of said first transistor and, when said first transistor is substantially turned on and thereby said third transistor as well is caused to be substantially fully conductive, the following voltage relationships exist:     V.sub.G2 =V.sub.BE2 +V.sub.BE3     where V BE3  is a voltage difference between the base and the second terminal of said third transistor and V G2  is a voltage to which said capacitor is charged and which functions as an equivalent gate voltage during the conductive state of all three said transistors.     
     
     
       2. The circuit of claim 1, the first transistor comprising a pnp transistor and the second and third transistors comprising npn transistors. 
     
     
       3. The circuit of claim 1, the first transistor comprising an npn transistor and the second and third transistors comprising pnp transistors. 
     
     
       4. The circuit of claim 1, comprising an integrated semiconductor circuit including said first, second and third transistors on a single chip. 
     
     
       5. The circuit of claim 4, said single chip semiconductor circuit further including said resistor therein. 
     
     
       6. The circuit of claim 4, said capacitor being a discrete element independent of said single chip. 
     
     
       7. The circuit of claim 6, said capacitor comprising a variable capacitor. 
     
     
       8. The circuit of claim 1 for use in series circuit with a switching element, a load and a power supply, wherein: said three transistors function as a switching device responsive to a signal of a first voltage level applied to said gate terminal to switch from an off to an on state, and said capacitor is charged during said on state for maintaining a higher turn-on voltage level on said gate than said first voltage level for a time interval determined in accordance with a discharge rate period defined by said resistor and said capacitor,   said switching element being subject to chattering and thereby interrupting the supply of power to said load from said power supply for corresponding, intermittent time periods, and   said resistor and capacitor being selected to define a time interval of discharge from said higher to said first voltage level which exceeds any such intermittent time period.   
     
     
       9. A circuit including an anode, a cathode and gate, said circuit connected to a power supply and ground via the anode and the cathode, said circuit comprising: a first transistor comprising a base, a first terminal connected to said gate, and a second terminal connected to a selected one of said anode and said cathode;   a second transistor comprising a first terminal connected to the base of the first transistor, a second terminal, and a base connected to the gate;   a third transistor having a first terminal connected to the first terminal of said second transistor, a second terminal connected to the other of said anode and said cathode, and a base connected to the second terminal of said second transistor;   a resistor, having a first end connected to the second terminal of said third transistor and a second end connected to the second terminal of said second transistor and the base of said third transistor to form a common node therewith, the common node being exclusively connected to said resistor and said second and third said transistors; and   a capacitor connected between said gate and the other of said anode and said cathode.